Wireless communication systems have become increasingly common. In such systems, a subscriber uses a local communication device, such as a portable cellular telephone, to communicate with a remote communication device, such as a cellular base station. Communication is accomplished via the transmission of radio frequency (RF) signals between the local device and the remote device.
To initiate communication, the local device communicates electronic information, such as an electronic serial number (ESN), to the remote device for registration. Upon receipt, the remote device determines whether the local device is permitted to make calls in the system based on the ESN. Aside from being used for limiting system access only to authorized users, the ESN is used for billing subscribers for calls made over the system.
In many wireless communication systems, the ESN is transmitted to the remote device in an un-encrypted manner and, thus, it is not secret and is susceptible to receipt by an unauthorized party. The unauthorized party may engage in fraudulent activity by programming the electronic information into, and making counterfeit calls via, a local device. Such fraud results in billing authorized subscribers for calls they did not make.
In the past, the risk of fraud was reduced by storing the ESN in a non-volatile memory device within a semiconductor device, such as an integrated circuit. More specifically, the ESN was stored in an EEPROM (electrically erasable programmable read only memory) that was internally disposed in a microcontroller employed by the local communication device. In operation, the EEPROM could not be accessed via the pinouts of the microprocessor and, thus, could not easily be reprogrammed or replaced with a "cloned" ESN.
However, combining an EEPROM on the same integrated circuit as a microcontroller is very expensive. The semiconductor manufacturing processes capable of providing non-volatile memory devices are expensive relative to those processes capable of providing logic circuitry only. Also, where the non-volatile memory and the logic circuitry are combined in a single microcontroller, yield reductions due to non-volatile memory programming failures can greatly increase the expense of the finished product.
Therefore, what is needed is an apparatus and method for securing electronic information, such as an ESN, that does not require the use of a non-volatile memory device packaged within a microcontroller device.